This invention relates to the purification of oxygen, and more particularly to the removal of low molecular weight hydrocarbons from an oxygen stream by adsorption at cryogenic temperatures.
Oxygen produced by conventional techniques such as the cryogenic distillation of air generally contains small amounts of low molecular weight hydrocarbons, such as methane, ethane, etc. For certain oxygen-consuming industrial processes, such as ozone production, it is important that the oxygen used as feed to the ozonizer be substantially free of hydrocarbons because hydrocarbons are converted to moisture and carbon dioxide in ozonizers, and the efficiency of ozonizers falls off rapidly as the dew point of the feed gas to the ozonizers increases.
Hydrocarbons can be removed from the oxygen feed stream to an ozonizer by various chemical or physical techniques. For instance, it is known to remove hydrocarbons from an oxygen stream by cryogenic distillation. This procedure requires the use of expensive equipment, such as distillation columns, heat exchangers, etc., which significantly increases the cost of the hydrocarbon-free oxygen product.
Hydrocarbons can also be removed from oxygen streams by reacting the hydrocarbons with oxygen over a suitable catalyst, such as platinum, thereby forming water and carbon dioxide. However, catalytic oxidation of the hydrocarbons is carried out at relative high temperatures, for example at temperatures up to about 400.degree. C. or higher; accordingly a significant quantity of energy is, expended in raising the temperature of the crude oxygen product to the reaction temperature. Furthermore, as noted above, the oxidation of hydrocarbons results in the production of significant amounts of moisture; accordingly, if it is desired to use this oxygen for ozone production, it is necessary to remove any water formed during the oxidation reaction prior to ozonization, or else settle for low ozone production efficiency.
U.S. Pat. No. 4,746,332 discloses the adsorption of oxygen from a nitrogen stream at cryogenic temperatures using sodium-exchanged A zeolite.
Because of the increasing need for hydrocarbon-free oxygen supplies, continuous efforts are being made to develop inexpensive and efficient processes for the removal of hydrocarbons from oxygen streams. The present invention provides such a process. The process of the invention can also effect the removal of other undesired gas components, such as nitrogen, from oxygen streams.